Bird Families

Willis hyperboles: an attempt at interpretation

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Universal Russian-German dictionary. Academic.ru. 2011.

  • helmet wang
  • helmeted oropendola

Species, it is not clear why too similar to each other

In connection with the discovery of the olingito, which for a long time was confused with the rather unrelated, but very similar beast of the olingo, I remembered this. Among the birds there are pairs of species, phylogenetically completely different, of different sizes, etc., however, with coloration that coincides to the smallest detail, what is the structure, what is filling.

Woodpeckers are especially numerous: see Martin L. Cody (1969). Say, woodpeckers from Southeast Asia Dinopium javanense and Chrysocolaptes lucidus (very different sizes, in the first species the paw is 3-fingered, in the second - 4x). Or from spotted woodpeckers are very similarly colored, but hairy of different sizes Dendrocopos villosus and fluffy Dendrocopos pubescens in North America. Another one was recently discovered: it was shown that the so-called. helmeted gall Dryocopos galeatus from the "Atlantic forests" of Southeast Brazil belongs to a different genus (and tribe) - the Celeus, and should be moved there.

“Although in color it is more similar to Dryocopus, the shape of the beak, nostrils and some small details of the plumage (for example, the white upper tail coverts) resemble Celeus... So, the beak of the helmeted gall is thinner, therefore it rarely hollows, - this unites it with the woodpeckers, but is not typical for actively destroying wood in search of food for the gall - owners of a powerful beak. "

A source elements.ru

However, the suggestion that “small woodpeckers mimic large ones in order to reduce their aggression” is purely speculative. It has long been expressed in two versions - this and the opposite in Cody: they say, different types of woodpeckers are therefore similar, because there is interspecific territoriality between them. Wherever they were specifically checked, they have not been confirmed.

Such couples unrelated up to a dozen species with matching coloration are known in birds (in diurnal carnivores, cuckoos, etc.), and this is if we ignore the cases of mimicry. The question for biologists is which of the factors of evolution can create and maintain such a complete similarity of color, moreover, about ecological proximity, similarity of size, biology, etc. the speech also does not go?

Or does this phenomenon require no special explanation, is it just a “tail” of the distribution describing the structure of diversity, say, the same Willis hyperbolas? That is, if in a large group of woodpeckers there are about 400 species, some integral similarity between them in color is distributed hyperbolically, well, 1% of the species will coincide in color very accurately. Which interpretation seems more likely to you?

Conclusion

Since the Willis curve reflects the structure of biodiversity, with its help it is possible to make predictions about the "degree of naturalness" of a system of approximately the same kind that is done using the "rank-size" rule (this is, in fact, the same rule), regarding the excess / deficiency of a given territory of urban settlements of different ranks and, accordingly, what they will do, grow or stagnate in the next period of time. Willis's rule makes it possible to assess the closeness of the existing classification of a group, taxonomic and meronomic (meron is a class of body parts, by comparing the same type of parts of organisms that make up each group, we extract the very same differential characters that distinguish the taxa included in it) to the "natural system" Which gives an argument in the eternal dispute between "splitters" and "unifiers", what about differentiable taxa, what about differentiating characters. And, among other things, this means that the profession of a taxonomist will be vital for a long time, since the studied systems "move in the direction of naturalness", although each of the groups contains indicators that "spoil the picture."

This also implies the idea of ​​the limited variability and taxonomic ranking of differential characters, so that the natural system is a fractal. Orderliness, i.e. the structure of biological diversity, independent of the phylogenetic history that generates it, the research of both turns out to be mutually complementary.

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